What Does the Helicopter’s Tail Rotor Do?

Most helicopters have a tail rotor at the end of the fuselage, image by Helen Krasner

Most helicopters have a small rotor placed vertically at the tail of the aircraft, which rotates continuously.

This has two main purposes: it prevents the helicopter fuselage from turning in circles continuously, and it is also used to control the helicopter’s direction when it is being flown.

Without a Tail Rotor, a Helicopter Would Turn in Circles!

To make a helicopter fly, the pilot raises the collective and increases the lift on the rotor blades in order to lift the helicopter into the hover.  However, this causes a definite problem.

If the blades are whirling anti-clockwise, as most helicopter blades do, the fuselage will start to rotate clockwise, due to torque reaction.  This is due to  Newton’s Third Law, which states that every action has an equal and opposite reaction. If you haven’t heard of this, one of the easiest ways of explaining it is to imagine a boat moored close to the shore.  If you are in the boat and push on the land, the land doesn’t move, but the boat does!

This is an example of Newton’s Third Law.

In the case of the helicopter, what can we do about this? Actually there are several ways of solving the dilemma. You can have two rotors that spin in opposite directions, as in the Chinook, and more recently, designers have experimented with blowing air out of ducts onto the tail boom to push it back, as it were.

But the most common method of preventing the fuselage spinning uncontrollably is to have a tail rotor. A small version of the main rotor, this is mounted vertically at the end of the tail cone, and it effectively works by pushing the tail back as the fuselage tries to rotate.  It is like a sideways rotor system, and the air being forced down between the blades is used to push the fuselage straight.

Using the Tail Rotor to Turn the Helicopter

We now also have a useful way of controlling the helicopter in yaw, that is movement around a vertical axis. This is done by altering the pitch angle of the tail rotor blades, ie changing by a small amount the degree of force or turning motion which they produce. This is done by means of the pedals, which are certainly not rudder pedals, as some fixed-wing pilots mistakenly believe.  The pedals are designed so that applying the left pedal turns the helicopter left, and applying right pedal turns it right.

Click to Read Page Two: Problems Caused by the Tail Rotor

© Copyright 2012 Helen Krasner, All rights Reserved. Written For: Decoded Science
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  1. says

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  2. Steve says

    Great article. > The primary function of the Tail Rotor, be it on a CW or CCW-turning rotorcraft, is to counteract the natural turning property of the fuselage caused by torque created when the engine forces the Main Rotor to rotate. The engine must push against something to force the Main Rotor to turn and that something is ultimately the fuselage. For example, a CCW-turning rotor (Bell 206) will cause the body of the aircraft to rotate CW. To counter the CW rotation of the fuselage, apply an appropriate amount of Left Pedal to cause the aircraft to maintain a fixed heading. It is a simple concept. Further, the Tail Rotor also causes the helicopter to drift away from the direction of its thrust (not its rotor-wash). A Bell 206 Tail Rotor will push the tail to the Right to counteract the Right rotation of the aircraft nose. If the Nose goes Right at the same amount that the Tail goes Right, the aircraft does not turn. That satisfies the rotation problem. But, the Right turning nose and Right thrusting Tail Rotor together cause the aircraft to Drift to the Right (of the fuselage’s longitudinal centerline). To maintain a constant spot over the surface at a hover, this Right Drift must be equally counteracted by an opposing Left Cyclic input sufficient to counter the Right Drift. It is as though the helicopter were being forced to fly sideways to the Left, but only enough to counter the Right Drift. A Bell 206 (in proper CG) will, therefore, hover at steady-state with a Low Left-side Rotor and Low Left Skid with a noticeable Left Cyclic. The Left Skid will be the first to touch the ground on landing and the last to leave the ground on lift-off to a hover. (Conversely, a CW-turning rotor system helicopter, i.e. Eurocopter, will hover Right-side Low). Also, as the helicopter (Bell 206) transitions from hover through translational lift and into flight, the Main Rotor and Tail Rotor dance an interesting duet, but after attaining steady-state cruise the Main Rotor will fly Higher on the Left and Rear and Low on the Right and Front of the disk. The Cyclic will tend to be to the Right and Forward of Center. >> I hope this has been helpful and not too boring. Also, if I have misrepresented anything, I welcome comment. sh/ 11-30-2012@0013.

  3. Cory Lovell says

    Didn’t Stanley Hiller discover this in 1944?
    “Stanley Hiller, Jr., was only a teenager when he opened the fourth American helicopter company and began mass-producing helicopters in 1948. The prelude to this milestone in vertical flight development was the design, construction, and flight of the first Hiller helicopter, the XH-44 (XH stands for ‘Experimental Hiller’, 1944 refers to the year the aircraft first flew). Hiller designed this rotorcraft to fly beneath twin rotors that counter-rotated about the same mast so there was no need for a tail rotor to control main rotor torque. A helicopter with coaxial rotors was unique among the American designs of that day and the XH-44 flew well enough to provide Hiller invaluable data.”

  4. says

    No matter what, but with taking off, the gyro and aerodynamic forces, has to be countered by cyclic. I did fly both, clock and counter-rotating rotors. In case of American helicopters it is from right forward toward the center, in Russians from left forward toward the center with lifting up collective and adding throttle. (By the way the throttle on the collective lever work reversed too). In Russia big helicopters has to be trimmed ass well according to manual. If you try to lift collective from ground with cyclic in center neutral, it is guaranteed that you will flip on your side and be lucky to talk about. As for pedals, they work like rudder on the fix wing airplane. Of course, to apply different forces, with the pedal movement, you are changing the pitch on that tail rotor prop.

  5. Walt says

    Not possible. I fly a Eurocopter A-Star 350BA. The A-Star and most European helicopters use clockwise rotation of the main rotor, while American-made helicopters use counter-clockwise rotation (as you look down on the helicopter). However, it doesn’t matter which way the main rotors turns as far as the pedal effects. Stepping on the right pedal causes the body of the helicopter to turn right. Anything else would be counter-intuitive and extremely difficult to control.

  6. Joe says

    Maybe it’s just me but last time I went up in a heli and I pressed my right foot forward on the pedals I rotated left or counter clockwise either way you look at it.

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